In recent years, the use of a user terminal (what is termed as a dual terminal) having both functions of cellular communication and wireless LAN (Local Area Network) communication is increasingly becoming popular. Further, the number of wireless LAN access points managed by an operator of a cellular communication system is increasing. Therefore, in 3GPP (3rd Generation Partnership Project) which is a project aiming to standardize a cellular communication system, a technology is being considered which is capable of strengthening linkage between a cellular RAN (Radio Access Network) and a wireless LAN.
For example, when switching is performed so that the traffic of a user terminal accommodated in a cellular RAN is accommodated in a wireless LAN, the traffic load of the cellular RAN can be reduced (offload). Further, as a network selection scheme of selecting, from the cellular RAN and the wireless LAN, an access network in which the traffic of a user terminal is transmitted and received, a plurality of schemes have been proposed (see Non Patent Literature 1).